Process for transferring lightpolarizing films from one support to another



as aizseiica accrue ucyu any avwn PROCESS FQR TRANSFERRING LIGHT POLAREZING FELMS FROM ONE SUPPQRT TO ANOTHER No Drawing. Application July 26, 1938, Serial Flu-221,349

. 3 Claims.

This invention relates to a new and improved process of transferring light-polarizing films or coatings from one support to another.

An object of the invention is to provide a process of the character described wherein a set suspension of oriented light-polarizing particles in a film-like, light-transmitting medium may be physically removed from a supporting plate or sheet and transferred to another support.

A further object of the invention is to provide a process of the character described wherein the transfer is effected by applying to the polarizing film to be transferred an adhesive, for example an adhesive comprising a softener or swelling agent for the film and exerting pressure between the object to be'coated and the film.

A still further object of the invention is to provide a process of the character described wherein the transfer of the polarizing film is effected between a pliable, preferably resilient, support and a rigid support.

Other objects of the invention will in part be" obvious and will in, part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others thereof which will be exemplified in the process hereinafter disclosed, and the scope of the application of which will be indicated in the claims.

It has heretofore been exceedingly diflicult to provide polarizing coatings for many light-transmitting or reflecting surfaces, particularly where the surfaces were non-planar or where it was desired to coat large elements, such as windows, mirrors and the like, without removing the elements from their places of use. A preferred type of polarizing material for use in the formation of such coatings is.a suspension of oriented lightpolarizing crystals in a transparent medium, such as is now available under the trade name Polaroid in exceedingly thin sheetswhich are admirably adapted for use in the present invention.

It is the object of this invention to provide. a

method whereby such thin films of light-polarizing material may be transferred and affixed to a support of any desired shape, whether concave,

convex or planar, and to provide such a method adapted for the coating of surfaces of large areas while those surfaces are positioned in the places in which they are to be employed.

Films of light-polarizing material of the above type may be readily formed, in any of a number of ways, on' smooth supporting plates or sheets; which in turnmay'be' flexible or pliable. A $115:-

pension of rod-shaped or needle-shaped polarizing particles in a light-transmitting medium may be prepared and orientation of the particles accomplished by smearing, painting, or rubbing the suspension upon the surface of a supporting sheet. It will be apparent that orientation may be accomplished in other ways, for example by extruding the suspension and depositing the film on a suitable support, or by applying the suspension to a support and stretching the support.

A preferred form of film of the above type for use in the present invention is one comprising a highly concentrated suspension of polarizing particles in a light-transmitting plastic. More specifically the preferred form of suspension for use in the present invention may comprise a suspension of particles of a herapathite-like kind, i.-e., polarizing compounds of quinine or cinchonidine, in a transparent plastic such as a cellulose ora vinyl compoundor the like. .7

A preferred support for the formationof a polarizing fihn from a suspension of the character described is a sheet or plate or film having a smooth and relatively hard planar surface. If a smearing or rubbing process is employed in the formation of the polarizing film, a highly satisfactory product can be secured by employing cellulose acetate as the material providing the surface upon which the suspension is rubbed or smeared and the polarizing film thus formed.

It is to be understood, however,- that other supports may be employed for the formation of the film, for example rubber, glass, a metallic surface such as a chromium-plated surface, Cellophane, or any surface of suitable smoothness and hardness and of a material which does not react with the suspended polarizing particles to destroy their polarizing properties, and which is not soluble in the solvent employed in the suspension of polarizing needles. Where a high concentration of the-polarizing compound in the light-transmitting plastlc is employed, the polarizing film formed therefrom may be exceedingly thin. Adequate polarization may be secured, for example, with films having a thickness less than .0003 inch. Thin films of this type are preferred.

In the process of the present invention a suit-. ably coated supporting plate or sheet, for example a sheet of cellulose acetate, Cellophane or the like, coated with a light-polarizing film of the character described, is employed, and the lightpolarizing film is transferred from the supporting sheet to another support in the manner hereinafter described.

A mixture of a solvent and a softener for the contact with the initial supporting sheet, and the polarizing film is pressed against the new support. This step should preferably take place substantially immediately, that is to say, before the softening action has progressed to an appreciable extent. The pressure employed need not be great, nor need it be applied for any extended period, but it should be smooth and even in order to guard against physically disorienting the polarizing particles in said film. As soon as the solvent and softener have had an opportunity of penetrating the film, and this occurs almost instantaneously, the cellulose acetate or other backing may be stripped from the polarizing film, leaving the film deposited upon the new support and, when the film dries, it will be found to be afiixed thereto and to adhere strongly thereto.

With a light-polarizing film of the character described and employing, for example, Vinylite XYSG as the suspending medium, a suitable solvent may be methanol, and a suitable softener may be ethyl acetate or butyl acetate. A preferred mixture for use in the process of this invention comprises approximately one part by volume of methanol to twelve parts by volume of ethyl acetate. Any substantially greater proportion of methanol may result in an undesired decomposition of the light-polarizing particles employed and an undesirable solution of the polarizing film itself. A mixture of methanol and ethyl acetate or butyl acetate in the proportions given may be applied in excess to the light-polarizing film without damaging the film.

In performing the process with the use of mixtures of a solvent and a softener, it will be understood that efiective transfers of the polarizing coating may be made from one support to another where the new support has a greater afilnity for the coating than the old support. It is to be understood, therefore, that the transfers are usually not reversible. Where cellulose acetate is used as the initial support, transfers may be made to a wide variety of products. For example, transfers may be made from cellulose acetate to rubber, 1 glass, vinyl acetal resin, paper, chromium-plated objects, steel, Cellophane, Bakelite, Celluloid, and glass coated with a thin' layer of Vinylite XYSG. It is to be understood that the examples given are not to be deemed all-inclusive. They are merely typical of many transfers which may be performed. Where the coating is first formed on glass, it may be transferred from the glass to a polymerized vinyl acetal resin.

'Where the coating is first formed on-rubber or is transferred from acetate to rubber, it may be transferred again to glass or to vinyl acetal resin. Where the coating is formed on Cellophane, or where it has been transferred to Cellophane from an acetate sheet, it may again be transferred toglass. Where the coating has been formed on a metallic surface, such as a chromium surface, it may be transferred to Cellophane and from Cellophane to glass.

It will be understood furthermore that the solvents and softeners employed in effecting the transfer may be, although they need not be, solvents or softeners for the support to which the polarized coating is to' be tansferred. Other solvents and softeners than those mentioned may be employed without departing from the scope of the invention. Speaking generally, it is desirable to use an excess of softener over solvent. Under certaincircumstances, a softener alone may be employed to effect the transfer.

Throughout this specification and the claims the application to a film of polarizing material of a softener therefor, or a mixture of a solvent and a softener therefor, will be defined as the application to the polarizing material of a volatile adhesive, for the effect of the solvent-softener mixture is to cause the polarizing layer or film to soften and swell slightly, so that it may be released from its initial support and caused to ad- .here to a new support. The'solvent employed is a volatile solvent and the softening agent also volatilizes, so that the mixture may properly be termed a volatile adhesive. In any event that phrase, where used throughout the specification and claims, is to be understood as including a softener alone, or a mixture of a solvent and softener for the film in which the polarizing particles are suspended. The term softener is to be understood as including-a swelling agent.

Other adhesives may be employed in effecting a transfer of the polarizing film from one to another support. In certain cases these adhesives may be non-volatile. A solution, for example, of

cellulose nitrate, and more specifically one-quarter second cellulose nitrate in ethyl acetate may be employed. If such a solution is appliedto the film of light-polarizing material and the film then pressed to a new supporting surface and dried, the initial support may be stripped away, leaving the film adhesively afiixed to the new support by means of a thin adhesive layer of cellulose nitrate. The ethyl acetate employed as the solvent for the cellulose nitrate adhesive evaporates, presumably through the polarizing film. In this connection it should be pointed out that while the cellulose nitrate has here been considered as being a non-volatile adhesive, it may be proper to consider the layer or film of cellulose nitrate as the new supporting element to which the polarizing film is transferred. If it is so considered, then the example given is to be deemed illustrative of the use of a softener alone. in effecting transfer.

Other suitable adhesives for use in the process just described are ethyl cellulose; Dow Plasticizer No. 6; Vinylite A, either alone or in combination with equal parts of one-quarter second cellulose nitrate and SanticizerB-lfi; a mixture of cellulose nitrate and Santicizer M-17 in the proportions for example of 10 grams ofcellulose nitrate to one o. c. f Santicizer; a mixture of 7 grams of cellulose nitrate, 5 grams of camphor and 2 grams of Santicizer M-1'7; a mixture of cellulose nitrate and Dow Plasticizer No. 6 in the proportions of 2 to l-by weight; vand a mixture of Vinylite A,

Santolite MHP, and Dow PlasticizerD-G in the proportions of 5 parts of the Vinylite, 5 parts of the Santolite and 1 part of the Dow Plasticizer by weight. In every case ethyl acetate may be employed as the solvent for the adhesive.

When adhesives of this kind are employed an adhesive film remains between .the polarizing film and the final support therefor, and the polarizing film adheres with-a firm bond to thesupport and may be somewhat hardened in the process of transfer. -When such adhesives are employed a 7 transfer may be effected from any surface on which the polarizing film has initially been formed to any other surface to which the adhesive layer will adhere.

Adhesives of the type just referred to are termed throughout this specification. and claims "non-volatile adhesives; Those listed are v not to as indicating generally the type of adhesive which may be employed in effecting the process of the 'be deemed all-inclusive, but are to be understood.

invention. It will be understood that in everycase the adhesive used should be one which is neither a solvent of nor reactive with the polarizing particles in polarizing film.

.If desired, d'esigns maybe formed in the coating before it is transferred from one support to another, as for example by cutting away or removing portions of the coating, or destroying the polarizing properties of the crystals in certain areas thereof, and the transfer may be effected in such a way as to carry over the design to the new support.

It will be apparent also that where the coating is deposited on a flexible or resilient support, such for example as rubber, transfer may be made to a curved surface, such for example as a convex or concave lens or mirror surface, or the surface of a glass bulb or the like, by pressing the resilient support against the curved surface.

films transferred may be non-uniform, i. e., it

may have the form of a design or may be of varying thickness. described are to be understood as illustrative of others of the sameclass that may be employed or accomplished.

Since certain changes may be madein carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The process comprising forming upon a suitable support an exceedingly thin film of a vinyl compound containing a high concentration or minute, needle-shaped light polarizing particles, orienting the needle axes of said particles to substantial parallelism simultaneously with the for- The materials and transfers mation of the film, and transferring said film from said first-mentioned support to a second support by applying between the contacting faces of said second support and said film an adhesive comprising a softener for said film, said ahesive being a non-solvent of said polarizing particles and pressing said second support evenly against said film before said film is appreciably softened.

2. The process comprising forming a light-polarizing film upon a supporting surface by apply ing to said surface a film of a transparent plastic containing a high concentration of light-polarizing minute needle-shaped particles and orienting the'needle axes of said particles to substantial parallelism simultaneously with the formation of the film, said film not exceeding .0093 inch in thickness, softening said film by applying thereto an adhesive comprising a solvent and softener for said film in such quantity only that the oriented needles within said film remain oriented, said adhesive being a non-solvent of said polarizing particles, and substantially immediately pressing evenly against said film a second supportcomprising material having a greater affinity than said first named support for said film, and removing said film from the first-mentioned' support by separating said supports, whereby-said film adheres to said second support.

3. The process comprising applying to a supporting surface a suspension of minute lights-polarizing particles of needle shape in a transparent plastic medium, forming from said suspension on said support an exceedingly thin film of said suspension and simultaneously orienting the needle axes of the polarizing particles to substantial parallelism within said thin film, applying to the exposed surface of said thin film a non-volatile adhesive comprising a softener for said film, the action of the softener upon the film being such that the oriented particles within the film retain their orientation, said softener being a non-solvent of and non-reactive with said particles, substantially immediately applying to the adhesively coated film a second supporting element and pressing it against said film and said'first support, said second supporting element comprising material having a greater affinity than said first support for said film, and strippin said film from said first support and causing it to adhere to said second support by separating said supports.

ROBERT P. BLAKE. 

